Wood and steel framing in buildings is mostly used in North America, Scandinavia, and Central Europe. Of interest ever since the energy crisis in the early 1970s in the United States is improvement in the thermal performance envelope (building envelope) afforded by such structural insulated framing systems. Building envelopes play an important role in the heat transfer between the exterior and the interior spaces of a building. From a thermal perspective, a well-performing building frame system is one that contributes to thermal comfort inside the building with minimum consumption of space conditioning energy. See Barrios et al., 2012, “Envelope wall/roof thermal performance parameters for non air-conditioned buildings,” Energy and Buildings 50 pp. 120-127 and ASHRAE, Energy-efficient Design of Low-rise Residential Buildings (ASHRAE Standard 90.2-2004), American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 1791 Tullie Circle NE, Atlanta, Ga. 30329, 2006, each of which is hereby incorporated by reference.
Building envelope technologies have been evaluated in the United States using techniques such a hot-box testing as well as numerical thermal analysis. Technical information, field and lab test thermal performance data, and three-dimensional thermal analysis from such evaluation provides for an objective evaluation of the existing building envelope technologies. For instance, R-values or U-values provide a measure of thermal performance of building envelope components. For building frame systems, the part of the frame that is traditionally analyzed is the cavity of the frame that is uninterrupted by details such as wooden or steel structural elements, windows, or vents, which comprises about 50-80% of the total area of the opaque building frame. For instance, in wall systems that make use of studs, this would be the stud cavities between studs. The remaining 20-50% of the wall area (e.g., the windows, studs, vents, etc.) is typically not analyzed when rating conventional insulation. As a result, for most forms of insulation, traditionally estimated R-values for such insulation are 20-30% higher than the corresponding overall whole wall R-values that are achieved when such insulation is used.
In principle, thermal performance of building frame assemblies has been increased conventionally by application of thicker and wider insulation space in building frame cavities, such as wall cavities, installing insulating sheathing, improving thermal resistance of insulation materials, reducing or eliminating thermal bridging, and/or applying airtight construction. Combinations of these methods is normally applied in practice to reach a high R-value and sometimes to improve other building performance aspects such as durability, constructability, and costs. For instance, Kosny et al. calculated that for wood-framed houses, 25 mm of EPS foam sheathing gives an average 7.3% of saving in that part of the whole building energy consumption which is generated by building enclosure. See, Kosny 2014, “A review of high R-value wood framed and composite wood wall technologies using advanced insulation techniques,” Energy and Buildings 72, pp. 441-456, which is hereby incorporated by reference.
One conventional wall technology that has been employed in wood frame building construction is exterior insulation finish system (EIFS). EIFS utilizes rigid insulation sheathing and plaster finish on the exterior wall surface. As illustrated in FIG. 1, EIFS walls typically consist of expanded polystyrene (EPS) board attached adhesively or mechanically to the structural sheathing boards and covered with a lamina composed of a modified cement base coat with woven glass fiber reinforcement and a textured colored finish coat. Thermal performance of EIFS wall is heavily dependent on the thickness of the exterior insulation applied. For example, using 100 mm thick EPS foam board with empty 2×4 wall stud cavity yields R-value of around RSI—3.5 m2 K/W. If cellulose or fiberglass insulation is added into the 2×6 wall stud cavity in addition to the 100 mm EPS foam board, the overall wall R-value of RSI—5.3 m2 K/W can be obtained. See Straube et al., 2009, “U.S. DOE Building America Special Research Project: High R Walls Case Study Analysis (Research Report-0903),” Building Science Press, Massachusetts, which is hereby incorporated by reference. It should be noted however that building codes in most North American jurisdictions have limited the maximum exterior foam insulation thickness to 100 mm due to fire performance issues emerged from fuel contribution of the insulation material. A historical drawback with EIFS has been moisture performance due to poor detailing practice related to water drainage. However, EIFS walls have been further developed and upgraded to overcome this issue. In fact, field monitoring and laboratory tests results have indicated that EIFS, being one of the most tested wall assemblies, demonstrates positive performance with respect to moisture management system and thermal control. See Karagiozis, 2006, “The Hygrothermal Performance of Exterior Wall Systems: Key Points of the Oak Ridge National Laboratory NET Facilities Research Project,” Report Prepared for EIMA Research Project, Oak Ridge National Laboratory, Tennessee, which is hereby incorporated by reference. After exposing these wall systems to real weather for thirty months, it was found that the best performing wall cladding was the EIFS wall with 100 mm of EPS insulation and a fluid-applied water-resistive barrier. It was also found from that study, that EIFS drainage assemblies using vertical ribbons of adhesive provide a drainage path and air space that contribute positively toward hygrothermal performance of walls. See Karagiozis, Id.
Further examples of conventional framing systems include double walls, Larsen truss walls, optimum or advanced framing walls, European walls, and walls with furring and composites. Such walls are framing systems are disclosed in Kosny 2014, “A review of high R-value wood framed and composite wood wall technologies using advanced insulation techniques,” Energy and Buildings 72, pp. 441-456, which is hereby incorporated by reference.
Given ever rising energy costs, and the ever present need for affordable housing, improved framing systems that provide satisfactory R-values without compromising other performance aspects such as durability, constructability, and costs, and that are compliant with applicable building codes are needed in the art.